Replace the full descriptions of reserved register fields by shorthands
with a negative field width, and merge adjacent reserved fields.

This reduces kernel size by 142 bytes.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1af5225c81ac871a461f7d824619275e2e0ed8df.1649865241.git.geert+renesas@glider.be